amend instruction to create py3_std

Modify this instruction to get first explain how to build a full running production environment called py3_std:

Then, create an environment called py3_std with lots of useful packages already included for a first start: ???

conda create -n py3_std -c conda-forge python=3 anaconda-client aospy basemap basemap-data-hires cartopy cdo cf_units cftime cmocean dask distributed eofs fortran-magic git git-lfs gsw haversine hdf5 ipython iris iris-sample-data jupyter line_profiler matplotlib memory_profiler mtspec nco netCDF4 numpy pandas pytables python-cdo scikit-learn scipy seaborn seawater spyder xarray ipykernel

This involves the necessity to include a new channel -n conda-forge, might be good to point that out in a commentary block!

Also, might be good to mention that one could build any kernels with any packages and this py3_std is just a suggestion to start with.